DatePicker Dialog defaultDate incorrect behaviour

The following code displays the defaultDate just fine:

<script type="text/javascript">
// Datepicker
$('.datepicker').datepicker({
   defaultDate: new Date(2010, 4, 25)
});
</script>

<div class="datepicker"></div>

However, as soon as I want to use the popup behaviour by changing the DIV element into a INPUT element, the defaultDate only gets a rollover state, which is gone as soon as I hover my mouse over the calendar (the javascript remains the same):

<input class="datepicker" />

I attached two screenshots of the situation: the first (correct) one displays an inline calendar with the selected date set to 25/5/2010 (although I initialized a Date() object with 25/4/2010, is this another bug?), the second (incorrect) one displays a popup calendar, where day 25 is merely hovered instead of selected.

I also attached index.html demonstrating the issue.

Thanks